1. Field of the Invention
The present invention relates to a load calculating device and a load calculating method which estimate a physical quantity relating to a failure phenomenon at least one place on an circuit board located in an electronic apparatus while the electronic apparatus is in operation, to execute a load calculation or fault diagnosis on the circuit board on the basis of the estimated physical quantity.
2. Related Art
Electronic apparatuses may be subjected to loads resulting from physical or chemical effects associated with a manufacture, test, or use environment. An electronics circuit board in the electronic apparatus may thus be damaged depending on the design thereof. For the electronics circuit board, it is expected that in response to demands for reduced size and thickness, improved performance, and multifunctionality, elements will be three-dimensionally mounted in the circuit board, components will be built into the circuit board, signals of greater capacities will be transmitted at higher speeds, and the elements generate a greater quantity of heat. Thus, the electronics circuit board may be at a higher risk for possible failures such as thermal fatigue damage to solder junctions, inappropriate insulation resulting from electromigration or whisker, element cracks, damage to micro-junctions, swelling or stripping of resin, and damage to wiring. Further, users' various purposes of utilization of the electronics circuit board further increase the uncertainty of the estimation of loads, which is important in reliability design. In the reliability design, the estimation of the load in a field (user specifications) is important in correctly understanding acceleration factors for reliability test conditions for field (user specification) conditions. However, for digital information apparatuses, users have various purposes of utilization, so that in more and more cases, the conventional estimation conditions for the field load fail to correspond to reality. Thus, a new method for reasonably calculating the field load is required. It is also important to inform the user of load history or a performance degradation condition while the apparatus is in use or when the apparatus is found faulty because this gives the user a feeling of security.
The failure phenomenon estimation problem involves a tradeoff between a plurality of failure modes and is complicatedly associated with a large number of parameters. It is thus difficult to determine how to deal with the problem only on the basis of local examinations. This is likely to result in the following ad-hoc determinations or actions without sufficient analysis of data structures; “the factors should be subjected to regressive analysis”, “the high correlation coefficient is expected to indicate a strong association”, “the average should to be taken in order to eliminate variations”, “this factor may have an impact and should thus be slightly weighted”, or “the physical quantity for a particular place should be used as a performance index”. For individual problems that have been sufficiently verified by failure phenomenon analysis, such an itemized design method often leads to high-performance processes owing to calibration data accumulated for many years. Further, such quick, responsive guidelines are important in a chaotic time of foundation. However, failure estimating methods or reliability designing methods overly adapted to the individual problems are often readily affected by a variation in circumstances or conditions. Furthermore, such a method has difficulty dealing quickly with new problems, possibly reducing general efficiency. It is thus important to provide uniform formulation for parts independent of the specialty of the problem as well as design guidelines for load and reliability modeling.
Related documents include Proc. 1974 Symp. on Mechanical Behavior of Material (T. Endo et al. (1974), pp. 371), Collected Papers of the Japan Society for Mechanical Engineers (Ippei USU, Hiroyuki OKAMURA, A, Vol. 44, No. 386, (1978), pp. 3322), and Hierarchical Bayes Model and Related Matters (Takashi MATSUMOTO, Makio ISHIGURO, Toshiro INUI, Kunishi TANABE, Iwanami Shoten, 2004).